1. Field of the Invention
The present invention relates to an apparatus for driving a ribbon of a printer, and more particularly to an apparatus for driving a ribbon of a printer, wherein a ribbon driving shaft is flexibly changed during printing respective colors while a multicolor ribbon consisting of at least two colors are moved up and down for smoothly winding the ribbon even under the state that a ribbon cartridge is lifted up to be sloped.
2. Description of the Prior Art
A small-sized printer is generally employed for a cash register for printing the item name, amount and so on over a sheet of paper 5 that is wound on a roll.
FIG. 1 is a diagrammatic section view showing a small-sized printer, in which a head 4 is installed at the inside of a printer main body 1, and a printing plate 6 is installed to be spaced from head 4 by a prescribed distance. A ribbon cartridge 2 is installed at the upper portion of printer main body 1 for placing a ribbon 3 between printing plate 6 and head 4. Ribbon cartridge 2 is furnished with a hub 2a for insertion of a ribbon driving shaft 7a, and ribbon 3 winds around hub 2a.
In connection with the small-sized printer formed as above, once ribbon driving shaft 7a is rotated while feeding sheet of paper 5 between printing plate 6 and head 4, ribbon 3 passes through head 4 while winding around hub 2a, thereby printing characters or numerals. In addition, since the ink covering ribbon 3 is used up during the printing operation, ribbon 3 should be moved.
Typically, a driven bevel gear 7 is installed to the lower portion of ribbon driving shaft 7a for moving ribbon 3, and a driving bevel gear 8 brought into meshing engagement with driven bevel gear 7 is furnished at one side of printer main body 1. Driven bevel gear 7 is fitted onto a gear shaft 7b formed at the lower portion of ribbon driving shaft 7a. A ratchet wheel 7d is formed along the upper inner periphery of driven bevel gear 7, and a ratchet 7c, brought into meshing engagement with ratchet wheel 7d, is formed along the outer periphery of gear shaft 7b. Driving bevel gear 8 is brought into meshing engagement with a motor which moves head 4 via a connection gear 8a, and ribbon driving shaft 7a is installed at one side of printer main body 1 via a bracket 7e.
In the conventional ribbon driving apparatus constructed as above, the rotating drive of the motor is transmitted to driving bevel gear 8 via connection gear 8a, and driven bevel gear 7 brought into meshing engagement with driving bevel gear 8 rotates gear shaft 7b. Once ribbon driving shaft 7a integrally formed with gear shaft 7b is rotated, hub 2a is rotated in one direction, and ribbon 3 passes through head 4 while winding around hub 2ap.
However, when using ribbon 3 constituted by a plurality of colors, it is disadvantageous in that the rotating force of ribbon driving shaft 7a is not smoothly transmitted toward hub 2a. In other words, if different first color 3a and second color 3b are respectively applied over the upper and lower sides of ribbon 3, first color 3a coincides with head 4 under the state that ribbon cartridge 2 is horizontally placed. At this time, hub 2a is fitted on ribbon driving shaft 7a in a vertical state to smoothly transmit the rotating force of ribbon driving shaft 7a, thereby incurring no restriction when moving ribbon 3.
Meantime, when the second color is to be used, ribbon cartridge 2 swings by centering about hub 2a to permit second color 3b of ribbon 3 to coincide with head 4. At this time, hub 2a is partially supported by being slantedly fitted on the end of ribbon driving shaft 7a because it cannot be smoothly moved in forward/backward and right/left directions because ribbon driving shaft 7a is secured to bracket 7e, thereby being disadvantageous in that the rotating force of ribbon driving shaft 7a cannot be smoothly transmitted.